I have a mechanical stainless steel caliper. This will be difficult to explain but here goes. When you open it up to measure a casing, the tips of the jaws (flat part, not the edged section) measure different from the part closest to the body. The same goes for the middle of the jaw. The caliper is new from cabelas. When the jaws are closed, they appear to be flush. Is this normal? Where should I take the measurement from? Any help would be nice. Thanks!